In a medical setting, oxygen can be delivered to a patient from a cryogenic vessel, high pressure gas storage vessel or other controlled pressure delivery sources, such as a hospital delivery system. Such an oxygen delivery system includes an adjustable flow regulator to select a flow rate of oxygen to the patient. Adjustable flow regulators typically include a circular orifice plate having a plurality of apertures of varying sizes through which the oxygen can flow.
In order to create an aperture that allows a certain flow rate, users of prior art techniques typically create an undersized aperture using a hand tool, measure the flow rate, and subsequently increase the aperture size and measure the flow rate until gas flows at the desired rate. Other prior art methods utilize needle valves, stamping or compression of a large aperture, fabrication and assembly of discrete components, blockage of a flow conduit by a ball or tapered pin, photoetching of a thin metal disk that is subsequently attached to a thicker plate, or other largely manual methods.
To obtain an accurate flow rate, a real-time flow measurement is therefore made of each aperture during fabrication. Because this is largely a manual process, accurate registration is difficult to achieve, sometimes yielding a secondary aperture proximate to the main aperture to produce the proper flow rate. If the flow rate of a particular aperture is greater than a desired flow rate, then the entire part is rejected.
Prior art techniques suffer from at least two disadvantages. First, they are time-consuming and labor intensive processes. Second, they do not take full advantage of the fact that flow rates are proportionally related to hole sizes.
Orifice plates can be manufactured having flow apertures that are formed to have accurate dimensions. As such, real-time measurement and repair is unnecessary. Consequently, every orifice plate can be identically fabricated, within allowed tolerances, using automated machinery. In addition, a complete flow control device can be manufactured from a single piece of materialxe2x80x94the orifice plate.
An orifice plate can include a rigid circular plate of material, such as brass or other soft metal, having a first (bottom) surface and a second (top) surface. A counter bore can yield a domed support structure in the material at each flow aperture location. Specifically, the domed support structure can have a partial ellipsoidal, or conical shape. In accordance with one aspect, the domed support structure has a semi-spherical shape. The counter bore thus defines a support structure having an open base at the first (bottom) surface and an apex proximate to the second (top) surface. Prior art attempts at piercing thin-walled orifice plates have failed due to the lack of such a support.
A flow aperture can then be formed through the material from the second (top) surface and registered to the apex of the support structure. In particular, there may be a plurality of apertures, each aperture having a respective size and registered to an apex of a respective support structure.
The support structures and the apertures can be created by a computer-controlled machine. In particular, the computer can control a piercing tool which is automatically registered to the apex of the support structure and inserted through the thinned material to form the flow aperture. By using a computer-controlled process, orifice plates can be repeatedly reproduced to be substantially identical, within permitted tolerance.
In accordance with a particular embodiment of the invention, the orifice plate can be used in a flow regulator. In a flow regulator, an inflow conduit provides oxygen or another gas at a substantially constant pressure and an outflow conduit provides the gas at a specific flow rate. The orifice plate is coupled between the inflow conduit and the outflow. In particular, the flow regulator can adjustably control the flow of medical oxygen from a supply vessel to a patient. In such an application, the flow apertures vary in size from about 0.0007 square millimeters or less to about 0.8 square millimeters and the thickness of plate material at the apex of the dome structure is about 0.1 millimeter. Flow rates of 1/32 liters per minute (lpm) can be reliably achieved from a 50 pounds per square inch (psi) oxygen supply. Other dimensions can be used for other applications.